EP1895835B1 - Using cytosine deaminases to diminish retroelement transfer from pigs to humans - Google Patents

Using cytosine deaminases to diminish retroelement transfer from pigs to humans Download PDF

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EP1895835B1
EP1895835B1 EP06785409.1A EP06785409A EP1895835B1 EP 1895835 B1 EP1895835 B1 EP 1895835B1 EP 06785409 A EP06785409 A EP 06785409A EP 1895835 B1 EP1895835 B1 EP 1895835B1
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cells
nucleic acid
apobec3g
porcine
apobec3f
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EP1895835A4 (en
EP1895835A2 (en
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Reuben S. Harris
Stefan R. Jonsson
Scott C. Fahrenkrug
Rebecca St. Claire Larue
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Recombinetics Inc
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Definitions

  • This invention relates to transgenic pigs and porcine cells that have decreased capability of transmitting retroelements such as porcine endogenous retroviruses to non-porcine cells and tissues, and more particularly to transgenic pigs and porcine cells that contain non-porcine cytosine deaminases.
  • Treating diabetes remains a substantial burden for patients and their families, with up to 50% of patients experiencing devastating secondary complications due to a lifetime of exposure to elevated glucose levels.
  • the islets of Langerhans either by the transplant of a vascularized pancreas or by the infusion of isolated islets.
  • suitable human pancreas donors are very rare. Pigs provide a potentially unlimited source of islets for xenotransplanation to diabetic patients, and can be developed to the point of clinical applicability, potentially well before other developing technologies, such as stem cells.
  • pig cells contain several types of ACTIVE retroelements called porcine endogenous retroviruses (PERVs). These agents are generally innocuous to the pig, but are of major concern for xenotransplantation.
  • ACTIVE retroelements porcine endogenous retroviruses
  • non-porcine cytosine deaminase polypeptides in pig cells and tissues.
  • expression of non-porcine cytosine deaminases e.g., human cytosine deaminases
  • porcine cells and tissues can facilitate control of the transmission of retroelements such as PERVs to human cells.
  • pigs cells and tissues that contain non-porcine cytosine deaminases have reduced capability of transmitting PERVs to human cells and as such, can reduce the risks associated with xenotransplantation from cross species gene transfer.
  • the invention as defined in the claims features a nucleic acid construct that includes a transcriptional unit, the transcriptional unit including a porcine regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deamineses polypeptide.
  • An inverted repeat of a transposon can flank each side of the transcriptional unit.
  • An insulator element also can flank each side of the transcriptional unit.
  • the nucleic acid construct further can include a nucleic acid sequence encoding a transposase.
  • the cytosine deaminase polypeptide of the disclosure can be selected from the group consisting of AID, APOBEC1, APOBEC2, APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, APOBEC3E, APOBEC3F, APOBEC3G, and APOBEC3H.
  • the cytosine deaminase polypeptide can be an APOBEC3F polypeptide such as a human APOBEC3F polypeptide or can be an APOBEC3G polypeptide such as a human APOBEC3G polypeptide.
  • the nucleic acid sequence encodes at least two cytosine deaminase polypeptides (e.g., an APOBEC3F polypeptide and an APOBEC3G polypeptide).
  • the porcine regulatory region can be a constitutive promoter or a tissue-specific promoter.
  • the invention as defined in the claims features an isolated porcine cell that includes a nucleic acid construct, the nucleic acid construct including a regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deaminase polypeptide.
  • the cell can be an embryonic cell, a fetal porcine cell (e.g., a fibroblast), an adult porcine cell (e.g., a dermal fibroblast), a germ cell (e.g., an oocyte or an egg), a stem cell (e.g., an adult stem cell or an embryonic stem cell), or a progenitor cell.
  • the invention as defined in the claims also features an isolated porcine cell that includes a non-porcine cytosine deaminase.
  • the cell further can include a nucleic acid encoding the non-porcine cytosine deaminase.
  • the cytosine deaminase polypeptide of the disclosure can be selected from the group consisting of AID, APOBEC1, APOBEC2, APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, APOBEC3E, APOBEC3F, APOBEC3G, and APOBEC3H.
  • the cytosine deaminase polypeptide can be an APOBEC3F polypeptide such as a human APOBEC3F polypeptide or can be an APOBEC3G polypeptide such as a human APOBEC3G polypeptide.
  • the nucleic acid sequence encodes at least two cytosine deaminase polypeptides (e.g., an APOBEC3F polypeptide and an APOBEC3G polypeptide).
  • the regulatory region can be a constitutive promoter or a tissue-specific promoter.
  • the invention as defined in the claims features a transgenic pig, cells derived from the transgenic pig, tissue isolated from the transgenic pig, and progeny of the Transgenic pig.
  • the nucleated cells of the pig include a nucleic acid construct, which includes a transcriptional unit that includes a regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deaminase polypeptide. Expression of the non-porcine cytosine deaminase polypeptide in at least some of the cells of the pig results, upon co-culture with human cells, in decreased capability of the cells to transmit porcine endogenous retroviruses to the human cells.
  • the regulatory region can be a constitutive promoter or a tissue-specific promoter.
  • An insulator element and an inverted repeat of a transposon can flank each side of the transcriptional unit.
  • the cytosine deaminase polypeptide of the disclosure can be selected from the group consisting of AID, APOBEC1, APOBEC2, APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, APOBEC3E, APOBEC3F, APOBEC3G, and APOBEC3H.
  • the cytosine deaminase polypeptide can be an APOBEC3F polypeptide such as a human APOBEC3F polypeptide or can be an APOBEC3G polypeptide such as a human APOBEC3G polypeptide.
  • the disclosure features a method for making a transgenic pig.
  • the method includes introducing a transgenic pig cell into an enucleated pig oocyte to establish a combined cell, the transgenic pig cell includes a nucleic acid construct, which includes a transcriptional unit that includes a regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deaminase polypeptide; producing a porcine embryo from the combined cell; transferring the porcine embryo to a recipient female; and allowing the porcine embryo to develop in the recipient female to produce the transgenic pig.
  • An insulator element and an inverted repeat of a transposon can flank each side of the transcriptional unit.
  • the disclosure also features a method of making a transgenic pig.
  • the method includes introducing a nucleic acid construct into a fertilized egg to produce an injected fertilized egg, where the nucleic acid construct includes a transcriptional unit that includes a regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deaminase polypeptide; transferring the injected fertilized egg to a recipient female; and allowing the injected fertilized egg to develop in the recipient porcine female to produce the transgenic pig.
  • the disclosure features a method for making a transgenic pig cell.
  • the method includes introducing a nucleic acid construct into a pig cell, the nucleic acid construct including a regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deaminase polypeptide.
  • the disclosure also features a method for making a transgenic pig cell.
  • the method includes introducing into a pig cell: a) a nucleic acid construct that includes a transcriptional unit, the transcriptional unit including a regulatory region operably linked to a nucleic acid sequence encoding a non-porcine cytosine deaminase polypeptide, wherein an insulator element and an inverted repeat of a transposon flank each side of the transcriptional unit; and b) a source of a transposase.
  • the source of the transposase can include a nucleic acid encoding the transposase.
  • the transposon and the source of the transposase can be present on separate nucleic acid constructs or on the same nucleic acid construct.
  • human cytosine deaminases such as APOBEC3G and 3F are capable of deaminating the genomic DNA of a eukaryotic cell.
  • Expression of APOBEC3G or its homolog APOBEC3F can inhibit the mobility of the retrotransposon Ty1 in Saccharomyces cerevisiae by a mechanism involving the deamination of cDNA cytosines.
  • the results described herein showing that APOBEC3F or -3G can inhibit yeast Ty1 retrotransposition were unexpected. Therefore, the Ty1 data described herein not only demonstrate the remarkable conservation of this mechanism but, importantly, they also show the mammalian factors (in addition to APOBEC3F or -3G) are not required for retroelement restriction.
  • cytosine deaminases in porcine cells reduces the capability of the porcine cells to transmit endogenous retroelements (e.g., retroviruses and retrotransposons) to the human cells.
  • endogenous retroelements e.g., retroviruses and retrotransposons
  • the invention as defined in the claims provides transgenic pigs and pig cells that express a non-porcine cytosine deaminase polypeptide. Organs and tissues from such transgenic pigs are useful for xenotransplantation due to the decreased risk of transmitting the endogenous porcine retroviruses to human cells relative to organs and tissues from pigs expressing endogenous cytosine deaminases.
  • cytosine deaminase polypeptide refers to any chain of amino acids, regardless of post-translational modification, that has the ability to deaminate cytosines to uracils within nucleic acid and that contains the following zinc-binding cytosine deaminase domain (amino acids provided in standard one-letter terminology): H/CXE (or another catalytic residue, e.g., D) X 20-30 PCX 2-4 C. See, Harris and Liddament (2004) Nat. Rev. Immunol. 4:868-877 .
  • Amino acid substitutions, deletions, and insertions can be introduced into a known zinc-binding cytosine deaminase domain and the resulting polypeptide is a "cytosine deaminase" provided that the polypeptide retains the ability deaminate cytosines to uracils.
  • Suitable non-porcine, mammalian cytosine deaminase polypeptides include single domain DNA cytosine deaminases and double domain DNA cytosine deaminases.
  • single domain DNA cytosine deaminases include, for example, activation induced deaminase (AID), APOBEC1, APOBEC2, APOBEC3A, APOBEC3C, APOBEC3D, APOBEC3E, and APOBEC3H polypeptides.
  • Double domain DNA cytosine deaminases include, for example, APOBEC3B, APOBEC3F, and APOBEC3G polypeptides.
  • APOBEC3D and APOBEC3E also can be produced as double domain cytosine deaminases. See, e.g., Harris and Liddament (2004), supra; and Jarmuz et al Genomics (2002) 79(3):285-96 .
  • APOBEC3G and/or APOBEC3F are particularly useful.
  • Human APOBEC3G apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G, also known as CEM15
  • CEM15 apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G, also known as CEM15
  • CEM15 apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G, also known as CEM15
  • CEM15 uses cytosine to uracil deamination to inhibit the replication of a variety of retroviruses, including HIV-1.
  • APOBEC3G localizes predominantly to
  • APOBEC3G In a retrovirus-infected cell, this localization may facilitate the incorporation of APOBEC3G into viral particles, which are released from the plasma membrane.
  • APOBEC3G also is specifically incorporated into virions through an association with the viral Gag protein and/or viral genomic RNA. Once a retrovirus enters a cell, its genomic RNA is reverse transcribed, and during this process, APOBEC3G is capable of deaminating cDNA cytosines to uracils (C - > U). These lesions occur at such a high frequency that they ultimately inactivate the virus (causing G -> A hypermutation, as read-out on the genomic strand of the virus).
  • APOBEC3F is a homolog of APOBEC3G and restricts HIV-1 infection by a similar mechanism.
  • APOBEC3F and -3G deaminate cytosines within different local contexts, preferring 5'- TC and 5'-CC, respectively.
  • the nucleic acid sequence encoding the cytosine deaminase can be a cDNA or can include introns or adjacent 5'- or 3'-untranslated regions (e.g., a genomic nucleic acid).
  • the nucleic acid sequence can encode a human APOBEC3F or APOBEC3G polypeptide.
  • GenBank Accession Nos. NM_145298 and NM_021822 provide the sequences of the human APOBEC3F and APOBEC3G cDNAs, respectively.
  • the nucleic acid sequence also can encode a sheep or cow APOBEC3F polypeptide as described herein.
  • the sheep and cow APOBEC3F proteins have an active amino terminal DNA cytosine deaminase domain, which elicits a broader dinucleotide deamination preference, and are fully resistant to HIV-1 Vif.
  • nucleic acid sequences having silent mutations that do not change the encoded amino acids or sequence variants that do change one or more encoded amino acids, but do not abolish enzymatic function also can be used.
  • the nucleic acid sequence of the ABOBEC3G used herein differs from the coding sequence of NM_021822 by a C to T transition at nucleotide position 588. This transition is silent and does not change the encoded amino acid at position 119 (F).
  • two or more cytosine deaminase polypeptides are encoded on the nucleic acid construct.
  • Nucleic acid constructs of the invention as defined in the claims include a nucleic acid sequence encoding a non-porcine cytosine deaminase.
  • nucleic acid includes DNA, RNA, and nucleic acid analogs, and nucleic acids that are double-stranded or single-stranded (i.e., a sense or an antisense single strand).
  • Nucleic acid analogs can be modified at the base moiety, sugar moiety, or phosphate backbone to improve, for example, stability, hybridization, or solubility of the nucleic acid.
  • Modifications at the base moiety include deoxyuridine for deoxythymidine, and 5-methyl1-2'-deoxycytidine and 5-bromo-2'-doxycytidine for deoxycytidine.
  • Modifications of the sugar moiety include modification of the 2' hydroxyl of the ribose sugar to form 2'-O-methyl or 2'-O-allyl sugars.
  • the deoxyribose phosphate backbone can be modified to produce morpholino nucleic acids, in which each base moiety is linked to a six membered, morpholino ring, or peptide nucleic acids, in which the deoxyphosphate backbone is replaced by a pseudopeptide backbone and the four bases are retained.
  • deoxyphospate backbone can be replaced with, for example, a phosphorothioate or phosphorodithioate backbone, a phosphoroamidite, or an alkyl phosphotriester backbone.
  • the nucleic acid sequence encoding the cytosine deaminase can be operably linked to a regulatory region such as a promoter. Regulatory regions can be porcine regulatory regions or can be from other species. As used herein, "operably linked” refers to positioning or a regulatory region relative to a nucleic acid sequence encoding a polypeptide in such a way as to permit or facilitate expression of the encoded polypeptide.
  • promoter can be operably linked to a nucleic acid sequence encoding a cytosine deaminase.
  • promoters include, without limitation, tissue-specific promoters, constitutive promoters, and promoters responsive or unresponsive to a particular stimulus. Suitable tissue specific promoters can result in preferential expression of a nucleic acid transcript in islet cells and include, for example, the human insulin promoter. Other tissue specific promoters can result in preferential expression in, for example, hepatocytes or heart tissue and can include the albumin or alpha-myosin heavy chain promoters, respectively.
  • a promoter that facilitates the expression of a nucleic acid molecule without significant tissue- or temporal-specificity can be used (i.e., a constituitive promoter).
  • a constituitive promoter such as the chicken ⁇ -actin gene promoter, ubiquitin promoter, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter, or 3-phosphoglycerate kinase (PGK) promoter
  • GPDH glyceraldehyde-3-phosphate dehydrogenase
  • PGK 3-phosphoglycerate kinase
  • viral promoters such as the herpes virus thymidine kinase (TK) promoter, the SV40 promoter, or a cytomegalovirus (CMV) promoter.
  • TK herpes virus thymidine kinase
  • CMV cytomegalovirus
  • a fusion of the chicken ⁇ actin gene promoter and the CMV enhancer is used as a promoter. See, for example, Xu et al. (2001) Hum. Genre Ther. 12(5):563-73 ; and Kiwaki et al. (1996) Hum. Genre Ther. 7(7):821-30 .
  • an inducible promoter is the tetracycline (tet)-on promoter system, which can be used to regulate transcription of the nucleic acid.
  • tet tetracycline
  • a mutated Tet repressor (TetR) is fused to the activation domain of herpes simplex VP 16 (transactivator protein) to create a tetracycline-controlled transcriptional activator (tTA), which is regulated by tet or doxycycline (dox).
  • tetR mutated Tet repressor
  • tTA tetracycline-controlled transcriptional activator
  • dox tetracycline-controlled transcriptional activator
  • Alternative inducible systems include the ecdysone or rapamycin systems.
  • Ecdysone is an insect molting hormone whose production is controlled by a heterodimer of the ecdysone receptor and the product of the ultraspiracle gene (USP). Expression is induced by treatment with ecdysone or an analog of ecdysone such as muristerone A.
  • Additional regulatory regions that may be useful in nucleic acid constructs, include, but are not limited to, polyadenylation sequences, translation control sequences (e.g., an internal ribosome entry segment, IRES), enhancers, inducible elements, or introns. Such regulatory regions may not be necessary, although they may increase expression by affecting transcription, stability of the mRNA, translational efficiency, or the like. Such regulatory regions can be included in a nucleic acid construct as desired to obtain optimal expression of the nucleic acids in the cell(s). Sufficient expression, however, can sometimes be obtained without such additional elements.
  • Signal peptides can be used such that the encoded polypeptide is directed to a particular cellular location (e.g., the cell surface).
  • selectable markers include puromycin, adenosine deaminase (ADA), aminoglycoside phosphotransferase (neo, G418, APH), dihydrofolate reductase (DHFR), hygromycin-B-phosphtransferase, thymidine kinase (TK), and xanthin-guanine phosphoribosyltransferase (XGPRT).
  • ADA adenosine deaminase
  • DHFR dihydrofolate reductase
  • TK thymidine kinase
  • XGPRT xanthin-guanine phosphoribosyltransferase
  • a nucleic acid sequence encoding a cytosine deaminase can include a tag sequence that encodes a "tag" designed to facilitate subsequent manipulation of the encoded polypeptide (e.g., to facilitate localization or detection).
  • Tag sequences can be inserted in the nucleic acid sequence encoding the cytosine deaminase polypeptide such that the encoded tag is located at either the carboxyl or amino terminus of the cytosine deaminase polypeptide.
  • End tags include green fluorescent protein (GFP), glutathione S-transferase (GST), and FlagTM tag (Kodak, New Haven, CT).
  • Nucleic acid constructs can be introduced into embryonic, fetal, or adult porcine cells of any type, including, for example, germ cells such as an oocyte or an egg, a progenitor cell, an adult or embryonic stem cell, a kidney cell such as a PK-15 cell, an islet cell, a ⁇ cell, a liver cell, or a fibroblast such as a dermal fibroblast, using a variety of techniques.
  • Non-limiting examples of techniques include the use of transposon systems, recombinant viruses that can infect cells, or liposomes or other non-viral methods such as electroporation, microinjection, or calcium phosphate precipitation, that are capable of delivering nucleic acids to cells.
  • transposon systems the transcriptional unit of a nucleic acid construct, i.e., the regulatory region operably linked to a nucleic acid sequence encoding a cytosine deaminase polypeptide, is flanked by an inverted repeat of a transposon.
  • transposon systems including, for example, Sleeping Beauty (see, U.S. Patent No. 6,613,752 and U.S. Patent Publication No. 20050003542 ), Frog Prince ( Miskey et al. (2003) Nucleic Acids Res. 31(23):6873-81 ), and Skipper have been developed to introduce nucleic acids into cells, including mice, human, and pig cells.
  • the Sleeping Beauty transposon is particularly useful.
  • a transposase can be encoded on the same nucleic acid construct or can be introduced on a separate nucleic acid construct.
  • Insulator elements also can be included in a nucleic acid construct to maintain expression of the cytosine deaminase polypeptide and to inhibit the unwanted transcription of host genes. See, for example, U.S. Patent Publication No. 20040203158 .
  • an insulator element flanks each side of the transcriptional unit and is internal to the inverted repeat of the transposon.
  • Non-limiting examples of insulator elements include the matrix attachment region (MAR) type insulator elements and border-type insulator elements. See, for example, U.S. Patent Nos. 6,395,549 , 5,731,178 , 6,100,448 , and 5,610,053 , and U.S. Patent Publication No. 20040203158 .
  • Viral vectors that can be used include adenovirus, adeno-associated virus (AAV), retroviruses, lentiviruses, vaccinia virus, measles viruses, herpes viruses, and bovine papilloma virus vectors. See, Kay et al. (1997) Proc. Natl. Acad. Sci. USA 94, 12744-12746 for a review of viral and non-viral vectors. Viral vectors are modified so the native tropism and pathogenicity of the virus has been altered or removed. The genome of a virus also can be modified to increase its infectivity and to accommodate packaging of the nucleic acid encoding the polypeptide of interest.
  • AAV adeno-associated virus
  • retroviruses retroviruses
  • lentiviruses lentiviruses
  • vaccinia virus measles viruses
  • herpes viruses herpes viruses
  • bovine papilloma virus vectors bovine papilloma virus
  • Adenoviral vectors can be easily manipulated in the laboratory, can efficiently transduce dividing and nondividing cells, and rarely integrate into the host genome. Smith et al. (1993) Nat. Genet. 5, 397-402 ; and Spector and Samaniego (1995) Meth. Mol. Genet., 7, 31-44 .
  • the adenovirus can be modified such that the E1 region is removed from the double stranded DNA genome to provide space for the nucleic acid encoding the polypeptide and to remove the transactivating E1a protein such that the virus cannot replicate.
  • Adenoviruses have been used to transduce a variety of cell types, including, inter alia, keratinocytes, hepatocytes, and epithelial cells.
  • Adeno-associated viral (AAV) vectors demonstrate a broad range of tropism and infectivity, although they exhibit no human pathogenicity and do not elicit an inflammatory response.
  • AAV vectors exhibit site-specific integration and can infect non-dividing cells.
  • AAV vectors have been used to deliver nucleic acid to brain, skeletal muscle, and liver over a long period of time (e.g., >9 months in mice) in animals. See, for example, U.S. Patent No. 5,139,941 for a description of AAV vectors.
  • Retroviruses are the most-characterized viral delivery system and have been used in clinical trials. Retroviral vectors mediate high nucleic acid transfer efficiency and expression. Retroviruses enter a cell by direct fusion to the plasma membrane and integrate into the host chromosome during cell division.
  • Lentiviruses also can be used to deliver nucleic acids to cells, and in particular, to non-dividing cells.
  • Replication deficient HIV type I based vectors have been used to transduce a variety of cell types, including stem cells. See, Uchidda et al. (1998) Proc. Natl. Acad. Sci. USA 95, 11939-11944 .
  • Non-viral vectors can be delivered to cells via liposomes, which are artificial membrane vesicles.
  • the composition of the liposome is usually a combination of phospholipids, particularly high-phase-transition-temperature phospholipids, usually in combination with steroids, especially cholesterol. Other phospholipids or other lipids may also be used.
  • the physical characteristics of liposomes depend on pH, ionic strength, and the presence of divalent cations. Transduction efficiency of liposomes can be increased by using dioleoylphosphatidylethanolamine during transduction. See, Felgner et al. (1994) J. Biol. Chem. 269,2550-2561 . High efficiency liposomes are commercially available. See, for example, SuperFect® from Qiagen (Valencia, CA).
  • transgenic pig includes founder transgenic pigs as well as progeny of the founders, progeny of the progeny, and so forth, provided that the progeny retain the nucleic acid construct.
  • a transgenic founder animal can be used to breed additional animals that contain the nucleic acid construct.
  • Tissues obtained from the transgenic pigs and cells derived from the transgenic pigs also are provided herein.
  • "derived from” indicates that the cells can be isolated directly from the pig or can be progeny of such cells.
  • brain, lung, liver, pancreas, heart and heart valves, muscle, kidney, thyroid, corneal, skin, blood vessels or other connective tissue can be obtained from a pig.
  • Blood and hematopoietic cells, Islets of Langerhans, ⁇ cells, brain cells, hepatocytes, kidney cells, and cells from other organs and body fluids for example, also can be derived from transgenic pigs.
  • Organs and cells from transgenic pigs can be transplanted into a human patient.
  • islets from transgenic pigs can be transplanted to human diabetic patients.
  • nucleic acid constructs into non-human animals to produce founder lines, in which the nucleic acid construct is integrated into the genome.
  • Such techniques include, without limitation, pronuclear microinjection ( U.S. Patent No. 4,873,191 ), retrovirus mediated gene transfer into germ lines ( Van der Putten et al. (1985) Proc. Natl. Acad. Sci. USA 82, 6148-1652 ), gene targeting into embryonic stem cells ( Thompson et al. (1989) Cell 56, 313-321 ), electroporation of embryos ( Lo (1983) Mol. Cell. Biol.
  • somatic cells such as cumulus or mammary cells, or adult, fetal, or embryonic stem cells
  • nuclear transplantation Wilmut et al. (1997) Nature 385, 810-813 ; and Wakayama et al. (1998) Nature 394, 369-374 ).
  • Pronuclear microinjection and somatic cell nuclear transfer are particularly useful techniques.
  • a nucleic acid construct described above is introduced into a fertilized egg; 1 or 2 cell fertilized eggs are used as the pronuclei containing the genetic material from the sperm head and the egg are visible within the protoplasm.
  • Linearized nucleic acid constructs can be injected into one of the pronuclei then the injected eggs can be transferred to a recipient female (e.g., into the oviducts of a recipient female) and allowed to develop in the recipient female to produce the transgenic pigs.
  • a transgenic pig cell such as a fetal fibroblast that includes a nucleic acid construct described above, can be introduced into an enucleated oocyte to establish a combined cell.
  • Oocytes can be enucleated by partial zona dissection near the polar body and then pressing out cytoplasm at the dissection area.
  • an injection pipette with a sharp beveled tip is used to inject the transgenic cell into an enucleated oocyte arrested at meiosis 2.
  • oocytes arrested at meiosis 2 are termed "eggs.”
  • the porcine embryo is transferred to the oviducts of a recipient female, about 20 to 24 hours after activation. See, for example, Cibelli et al. (1998) Science 280, 1256-1258 and U.S. Patent No. 6,548,741 .
  • Recipient females can be checked for pregnancy approximately 20-21 days after transfer of the embryos.
  • Standard breeding techniques can be used to create animals that are homozygous for the cytosine deaminase polypeptide from the initial heterozygous founder animals. Homozygosity may not be required, however, to observe a decreased capability of transmitting PERV to human cells.
  • cytosine deaminase polypeptides can be assessed using standard techniques.
  • Initial screening can be accomplished by Southern blot analysis to determine whether or not integration of the construct has taken place.
  • Southern analysis see sections 9.37-9.52 of Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, second edition, Cold Spring Harbor Press, Plainview; NY .
  • Polymerase chain reaction (PCR) techniques also can be used in the initial screening. PCR refers to a procedure or technique in which target nucleic acids are amplified.
  • sequence information from the ends of the region of interest or beyond is employed to design oligonucleotide primers that are identical or similar in sequence to opposite strands of the template to be amplified.
  • PCR can be used to amplify specific sequences from DNA as well as RNA, including sequences from total genomic DNA or total cellular RNA.
  • Primers typically are 14 to 40 nucleotides in length, but can range from 10 nucleotides to hundreds of nucleotides in length. PCR is described in, for example PCR Primer: A Laboratory Manual, ed. Dieffenbach and Dveksler, Cold Spring Harbor Laboratory Press, 1995 .
  • Nucleic acids also can be amplified by ligase chain reaction, strand displacement amplification, self-sustained sequence replication, or nucleic acid sequence-based amplified. See, for example, Lewis (1992) Genetic Engineering News 12,1 ; Guatelli et al. (1990) Proc. Natl. Acad. Sci. USA 87, 1874-1878 ; and Weiss (1991) Science 254, 1292-1293 .
  • a nucleic acid sequence encoding a cytosine deaminase polypeptide in the tissues of transgenic pigs can be assessed using techniques that include, without limitation, Northern blot analysis of tissue samples obtained from the animal, in situ hybridization analysis, Western analysis, immunoassays such as enzyme-linked immunosorbent assays, and reverse-transcriptase PCR (RT-PCR).
  • a non-porcine cytosine deaminase polypeptide in at least some of the cells of the pig can result, upon co-culture with human cells, in a decreased capability of the cells to transmit PERV to the human cells.
  • Transgenic pig cells and human cells can be physically separated by a thin membrane with 1 micron-sized pores and co-cultured for approximately 50 generations or 25 days. Such a membrane permits free diffusion of small molecules including viral particles but does not permit diffusion of cells.
  • the human cells can be harvested and tested for PERV reverse transcriptase activity (as a measure of infectivity) using an ELISA assay (e.g., from Cavidi Tech, Uppsala, Sweden). It is understood that a particular phenotype in a transgenic animal typically is assessed by comparing the phenotype in the transgenic animal to the corresponding phenotype exhibited by a control non-human animal that lacks the transgene.
  • Transgenic pigs of the invention as defined in the claims can be bred with other animals of interest (e.g., animals with transplantation-compatible backgrounds such as pigs with an inactivated ⁇ -1,3 galactosyl transferase gene).
  • the resulting progeny animals may be particularly useful for xenotransplantation due to the decreased risk of transmitting endogeneous retroviruses to human cells and the decreased risk of hyperacute rejection.
  • Such animals can be produced by, for example, crossing (a) a transgenic pig expressing a non-porcine cytosine deaminase polypeptide with (b) a transgenic pig with an inactivated ⁇ -1,3 galactosyl transferase gene.
  • a single line or transgenic pigs can be produced by initially preparing the pigs using the appropriate transgenes.
  • Yeast Strains were done in L40 (MAT ⁇ his3 ⁇ 200 trp1-901 leu2-3112 ade2 LYS2::(lexAop) 4 -HIS3 URA3::(lexAop) 8 -lacZ GAL4) (1). Retrotransposition assays were done in DG1251 ( MATa ura3-167 trp1-hisG spt3-101 his3 ⁇ 200 ) or GRY1990, a derivative of DG1251 in which E .
  • coli ⁇ -galactosidase is constitutively expressed from the yeast PGK1 promoter ( Nissley et al., (1996) Nature 380, 30 ; Nissley et al. (1998) Proc. Natl, Acad. Sci. USA 95, 13905-10 ).
  • Endogenous retrotransposition assays were carried in DG1141 [ MAT ⁇ trp1-hisG ura3-167 his3 ⁇ 200 Tyl-2y2his3A1; ( Curcio and Garfunkel (1991) Proc. Natl. Acad. Sci. USA 88, 936-40 ).
  • L40 ung1::kanMX4 was constructed by amplifying the ung1::kanMX4 cassette from yeast deletion strain 36067 (R. Wright, University of Minnesota), transforming L40 with the resulting PCR product and selecting G418-resistant colonies ( Wach et al. (1994) Yeast 10, 1793-1808 )). ung1 deletion was conformed by PCR and screening for a modest CAN1 mutator phenotype.
  • Plasmids Plasmids. Constructs were based on pHybLex-Zeo or pJG4-5 (Invitrogen, Carlsbad, CA).
  • the LexAAPOBEC3G fusion protein was constructed by subcloning APOBEC3G from pAPOBEC3G-IRES-bleo ( Harris et al. (2003) Cell 113, 803-809 ) using Not I and Pst I.
  • Untagged APOBEC3G in pHybLex- Zeo contains a 5 bp insertion between the LexA and APOBEC3G open reading frames.
  • Ugi was subcloned from pEF-Ugi ( Di noisya and Neuberger (2002) Nature 419, 43-48 ) as an Eco RI and Not I fragment into pcDNA3.1 (Invitrogen). It was subcloned into pYES3-CT using Hind III and Not I (Invitrogen). Ugi expression was confirmed using the CAN1 mutation assay.
  • the wild-type HIV-1 Vif sequences were amplified by PCR from HIV-1 YU-2 and IIIB proviral plasmids (M. Malim, Kings College London), digested with Nco I and Bam HI and were first cloned into similarly cut pTrc99A (AP Biotech).
  • Vif was subsequently subcloned into pHybLex-Zeo using a Nco I and Pst I digest and finally into pJG4-5 using EcoRI and Sph I.
  • APOBEC3F was subcloned from pTrc99A-APOBEC3F ( Liddament et al. (2004) Curr. Biol. 14, 1385-1391 ) into both pHybLex-Zeo and pJG4-5 using Eco RI and Sal I.
  • Ty1 Retrotransposition Assays Ty -his3AI, TyHRT- his3AI, Ty -lucAI or TyHRT- lucAI plasmids were co-transformed with pJG4-5, pJG4-5-APOBEC3G or pJG4-5-APOBEC3F into DG1251 or GRY1990 ( Gietz et al. (1995) Yeast 11, 355-360 ) and selected using SC-URA-TRP+GLC.
  • his3AI transformants were grown in SC-URA-TRP+GLC to saturation. Approximately 10 6 cells were subcultured in 1 ml of SC-URA-TRP+GAL for 12 hrs and an aliquot was plated to SC-HIS. Cell viability was determined by plating a dilution to rich medium. Retrotransposition was quantified by determining the frequency of His+ colonies.
  • lucAI transformants were grown 1 day in SC-URA-TRP+GLC. Cells were transferred to SC-URA-TRP+GAL and grown for an additional 2 days at 30°C to induce retroelement expression and reverse transcription. Retrotransposition was quantified by measuring the relative active levels of luciferase to ⁇ -galactosidase. All incubations for plasmid-based Ty1 assays were at 30°C.
  • DG1141 was transformed with pJG4-5, pJG4-5-APOBEC3G, or pJG4-5-APOBEC3F.
  • Single colonies were resuspended in water and 10-50,000 cells were transferred to 2 mL SC-TRP+GAL and grown at 20°C for 7-10 days until the cultures reached saturation. Dilutions of the starting and ending cultures were plated to rich media to determine the number of viable cells and the equivalent of 1 mL of the saturated culture was plated to SC-HIS to score retrotransposition events.
  • Ty1 DNA Sequencing Retrotransposed Ty1 and TyHRT cDNAs were isolated by growing His + colonies overnight in 10 ml SC-HIS at 30°C and preparing DNA with a standard glass bead/phenol extraction method. The resulting DNA was used to amplify a 1,026 (Ty) or 971 (TyHRT) bp region spanning the RT gene and HIS3 using 5'-TTC ATG TGG GAC ACT AGA GAT (TyRT, SEQ ID NO:1) or 5'-CCT GAG TGG GAG TTG TTA (TyHRT, SEQ ID NO:2) and 5'-TAT GAT ACA TGC TCT GGC CAA (HIS3, SEQ ID NO:3).
  • PCR products were purified (Qiagen) and sequenced with 5'-GT CTG CGA GGC AAG AAT GAT (SEQ ID NO:4).
  • GFP-negative retrotransposition events were obtained from pools of His + colony genomic DNA by transformation into E. coli. GFP-negative colonies were identified using fluorescent light and the resident plasmid DNA was amplified (as above except the product was 2.1 kb for Ty RT) and sequenced using 5'-C GTT ATC CGG ATC ATA TGA (SEQ ID NO:5) and 5'-G TAG TTC CCG TCA TCT TGA (SEQ ID NO:6).
  • APOBEC3G Stimulates Mutation in Saccharomyces cerevisiae via the Uracil Excision Pathway
  • a LexA-APOBEC3G fusion protein was expressed in the haploid strain L40 and the accumulation of mutations that conferred resistance to the toxic amino acid canavanine was monitored. Liquid cultures were grown from individual colonies expressing APOBEC3G or a control vector and then plated onto a solid medium containing canavanine. The numbers of canavanine-resistant (Can R ) colonies were determined after 3-4 days growth.
  • yeast expressing both APOBEC3G and a uracil DNA glycosylase inhibitor (Ugi) protein showed a 320-fold increase in the median frequency of mutation to CanR ( FIG 1B ). This stimulation was approximately 6-fold and 26-fold higher than that observed in LexA-APOBEC3G-expressing and in Ugi-expressing yeast cells, respectively, indicating that many of the APOBEC3G-dependent uracils were repaired by a uracil excision mechanism.
  • Unglp uracil DNA N-glycosylase 1 protein
  • Ungi uracil DNA N-glycosylase 1 protein
  • Ugi-resistant uracil excision activities occur in mammalian cells, such as those elicited by the SMUG1 and TDG1 proteins (Barnes and Lindahl (2004) supra ).
  • homologous recombination was used to construct an Unglp deletion strain, L40 ung1::kanMX4.
  • APOBEC3G is localized predominantly to the cytoplasm of mammalian cells. Therefore, it was surprising that its expression in yeast caused high mutation frequencies. To ensure that the high mutation frequencies were not attributable to the DNA binding properties of the LexA tag, the CAN1 mutation frequency was monitored of cells expressing either LexA-APOBEC3G or untagged APOBEC3G. Little difference in the overall median frequencies of Can R mutation was observed demonstrating that the DNA binding domain of LexA was not responsible for the APOBEC3G-dependent mutator phenotype ( FIG 1B ).
  • APOBEC3G Triggers Predominantly C/G -> T/A Transition Mutations in Yeast
  • CAN1 encodes a membrane-spanning arginine transporter that must be inactivated for growth to occur in the presence of the toxic arginine analog canavanine.
  • a wide variety of base substitution, insertion, deletion and more complex mutations can confer Can R [e.g., ( Huang et al., (2003) Proc. Natl. Acad. Sci. USA 100, 11529-11534 ; Rattray et al (2002) Genetics 162,1063-1077 ].
  • the CAN1 gene of a large number of Can R colonies was sequenced.
  • Yeast lacking Ung1p due to Ugi expression also displayed an increased level of C/G -> T/A transition mutations (64%), as would be expected of cells lacking uracil excision repair ( FIG 4C-4D ). However, 5/7 of these transitions occurred at positions that were not mutated in APOBEC3G expressing cells. Co-expression of Ugi and APOBEC3G resulted in an even stronger C/G -> T/A transition bias (95%), and 19/21 of these mutations occurred at sites that were also mutated in APOBEC3G expressing (Ugi negative) yeast cells ( FIG 4C-4D ). These data further demonstrated that APOBEC3G is capable of triggering genomic hypermutation in yeast by a C -> U deamination mechanism.
  • HIV-1 Vif derived from the YU2 or the IIIB provirus
  • APOBEC3G yeast two-hybrid bait or prey vectors. All possible pairwise combinations were tested for the ability to drive the yeast two-hybrid reporter genes lacZ or HIS3. No significant ⁇ -galactosidase activity or histidine prototrophy was observed despite repeated attempts (data not shown). This result was not attributable to an expression failure as both proteins could be detected in cell lysates by immunoblotting.
  • the sensitive CAN1 mutation assay might provide a more robust method for monitoring this interaction.
  • the Can R mutation frequencies of cells co-expressing Vif and APOBEC3G were compared with those of cells expressing either protein alone.
  • the robust hypermutability of APOBEC3G was not significantly affected by HIV-1 Vif co-expression. Therefore, a Vif-APOBEC3G interaction in yeast was not detected.
  • Ty1 RNA expression, splicing, reverse transcription and integration yield functional reporter gene cDNA copies, encoding either histidine prototrophy or luciferase activity.
  • Ty1-his3AI The ability of Ty1-his3AI to retrotranspose was monitored in the presence of human APOBEC3F or -3G ( FIG 6B ). In comparison to cells containing a control vector, an average of 51 % or 70% fewer His + colonies were detected in the presence of APOBEC3F or -3G, respectively. Slightly larger APOBEC3-dependent declines in Ty1- lucAI retrotransposition were observed, as monitored by the relative levels of luciferase present in liquid cultures ( FIG 6C ).
  • TyHRT integration occurs predominantly by homologous recombination, whereas Ty1 integration mostly uses its own integrase. Retrotransposition of both TyHRT -HisAI and TyHRT- lucAI (i.e., the accumulation of HIV-1 reverse transcriptase products) was also inhibited by APOBEC3F or APOBEC3G expression ( FIG 6D, E ).
  • a modified version of the Ty-his3AI system was used in which a GFP cassette was placed upstream of his3AI ( FIG 8A ). This enabled the selection of His + integrants and a subsequent screen for unselected GFP-negative variants. Twenty independent GFP mutants were recovered from retrotransposition experiments in which APOBEC3G was expressed. Each sequence contained at least one mutation and as many as 15 mutations. In total, 57 base substitution mutations were identified and 47 of these were minus strand C -> T transitions ( FIG 8B , FIG 9A ).
  • a construct for expression of human APOBEC3G was produced using the cytomegalovirus (CMV) promoter to drive expression and the neomycin gene as a selectable marker.
  • CMV cytomegalovirus
  • the construct was stably introduced into pig kidney PK-15 cells (ATCC # CCL-33) using Fugene® 6 reagent (Roche Applied Science, Indianapolis, IN) and cells were selected for neomycin resistance.
  • PK-15 cells were chosen for these experiments because the PERVs residing in these cells were able to infect human 293T cells in simple supernatant mixing experiments ( Patience et al., (1997) Nat Med 3, 282-286 ).
  • PERVs can transmit as solution-soluble cell-free particles and/or through cell-cell contact.
  • APOBEC3G expression in PK-15 cells was confirmed using specific antibodies ( Newman et al. (2004) Curr Biol. 15(2):166-70 ).
  • PK-15 cells expressing a vector control, human APOBEC3G (hA3G), or pig APOBEC3F (SsA3F) were co-cultured with human 293T cells for 25 days (approximately 50 cell generations); the two cell types were physically separated by a thin membrane with 1 micron-sized pores, which permitted free diffusion of small molecules including viral particles but it did not permit diffusion of cells. After 25 days, whole cell protein extracts were prepared from the 293T cells using standard procedures.
  • RT reverse transcriptase activity
  • FIG 10 Results in FIG 10 are shown as relative fold inhibition of RT activity normalized to RT activity in 293T cells cultured with PK-15 cells expressing an empty vector. This experiment indicates that expression of human A3G (but not expression of additional pig APOBEC3F) in PK-15 cells inhibits PERV transfer from PK-15 cells to 293T cells.
  • Semi-quantitative and quantitative, real-time PCR assays were performed to monitor for the presence of integrated PERV DNA in human 293T cells.
  • Semi-quantitative PCR was performed using 75 ng of template genomic DNA from human 293T cells and primers (forward 5'-AA CCC TTT ACC CTT TAT GTG GAT-3', SEQ ID NO:2; reverse 5'-AA AGT CAA TTT GTC AGC GTC CTT-3', SEQ ID NO:3) made to the PERV pol gene (product size: 196 bp).
  • primers forward 5'-AA CCC TTT ACC CTT TAT GTG GAT-3', SEQ ID NO:2; reverse 5'-AA AGT CAA TTT GTC AGC GTC CTT-3', SEQ ID NO:3
  • product size 196 bp
  • PCR also was performed using primers specific to pig DNA (forward 5'-GG AAC CTG CAA CCT ATG GAA-3', SEQ ID NO:4; reverse 5'-GG TGT GGC CCT AAA AAG ACA-3', SEQ ID NO:5) (351 bp product).
  • the left panel of FIG 11B shows that no pig PCR products were detected in 293T samples from the co-culture experiment.
  • the right panel contains positive and negative controls. Micro-chimerism was not detected.
  • Quantitative, real-time PCR assays were performed in 25 ⁇ L reactions containing 10 ng of 293T genomic DNA, 100 nM primers, and 2x iQ SYBR Green super mix (BioRad, Hercules, CA) and run on an iCycler iQ Multicolor Real-Time PCR detection System (BioRad, Hercules, CA). Thermocycler conditions were 95°C for 5 min followed by 50 cycles of 95°C for 15 seconds and 60°C for 30 seconds. A melting curve analysis directly followed the cycling to verify amplification of the PERV pol gene PCR product (amplified as discussed above).
  • the human beta-actin gene (housekeeping gene) was amplified as an internal control using the following primers : Forward, 5'-AT CAT GTT TGA GAC CTT CAA-3' (SEQ ID NO:6) and reverse, 5'-A GAT GGG CAC AGT GTG GGT-3' (SEQ ID NO:7) (product size: ca. 100 bp). All data were normalized and PERV gene copies are presented per 100,000 beta-actin copies ( FIG 12 ). PERV transfer was apparent after 20 days of continuous co-culture in the vector control cells, whereas little transfer occurred in the presence of human APOBEC3G. Thus, expression of human APOBEC3G in pig PK-15 cells inhibited PERV transfer from pig PK-15 cells to human 293T cells.
  • NCBI BLAST searches were performed using the human and mouse A3 deaminase domains as query polypeptides.
  • Several artiodactyl (cloven hoof ungulates) ESTs were identified, which suggested the presence of at least one A3 protein in cattle ( Bos taurus (Bt), GenBank Accession No. BE684372, Smith et al, Gen. Res. 11(4): 626-630, 2001 ) and pigs ( Sus scrofa (Ss), GenBank Accession No. BI346898, Fahrenkrug et al., 2002, Mamm Genome, 13, 475-478 ).
  • Corresponding cDNA clones were obtained, sequenced and shown to encode A3 proteins with two putative zinc-binding, cytosine deaminase domains.
  • the orthologous sheep ( Ovis aries, Oa) double domain A3 cDNA sequence was obtained using a combination of degenerate PCR and nested 3' prime RACE. All three of these A3 proteins were similar in size to the 373 amino acid HsA3F protein, except the pig A3 protein, which was slightly longer due to a unique C-terminal, serine-rich extension.
  • BtA3F The cow, sheep, and pig A3 proteins are referred to herein as BtA3F (SEQ ID NO:8), OaA3F (SEQ ID NO:9) and SsA3F (SEQ ID NO:10), respectively.
  • SEQ ID NO:8 The cow, sheep, and pig A3 proteins are referred to herein as BtA3F (SEQ ID NO:8), OaA3F (SEQ ID NO:9) and SsA3F (SEQ ID NO:10), respectively.
  • SsA3F SEQ ID NO:8
  • OaA3F SEQ ID NO:9
  • SsA3F SEQ ID NO:10
  • Rifampicin resistance is attributable to base substitution mutations in the E. coli RNA polymerase B ( rpoB ) gene, and it occurs in approximately one of every five million bacterial cells. This assay therefore provides a robust measure of intrinsic DNA cytosine deaminase activity. See, for example, Haché et al. (2005) J Biol Chem, 280, 10920-10924 ; Harris et al. (2002) Molecular Cell, 10, 1247-1253 .
  • Artiodactyl A3F DNA cytosine deamination preferences were examined by sequencing the rpoB gene of at least 100 independent RifR mutants. In contrast to HsA3F and HsA3G, which preferentially deaminate cytosines at rpoB nucleotide positions 1721 and 1691, 5'-TC and 5'-CC, respectively, the artiodactyl A3F proteins showed less biased rpoB mutation spectra. OaA3F preferentially deaminated cytosine 1576, which is part of a 5'-GC dinucleotide. SsA3F also preferred cytosine 1576.
  • SsA3F also clearly deaminated cytosine 1586, which is part of a 5'-AC dinucleotide.
  • the main conclusion from the RifR mutation assays was that all three of the artiodactyls A3F proteins were capable of deaminating DNA cytosines and triggering a corresponding shift in the pattern of C/G -> T/A transition mutations within the rpoB mutation substrate.
  • the sub-cellular distribution of these proteins was determined by live cell fluorescence microscopy. Approximately 7,500 HeLa cells were seeded on LabTek chambered coverglasses (Nunc). After 24 hrs of incubation, the cells were transfected with 200 ng of the pEGFP-A3-based DNA constructs. After an additional 24 hrs of incubation, images of the live cells were collected using a Zeiss Axiovert 200 microscope at 400x total magnification.
  • HsA3B and an eGFP control which localized to the nucleus and the entire cell, respectively, the artiodactyl A3F proteins and MmA3 (mouse) were predominantly cytoplasmic, with punctate bodies apparent in some cells. This pattern of localization is identical to that seen for HsA3F and HsA3G, indicating that the artiodactyl A3F proteins might similarly function to inhibit the replication of LTR-dependent retroviruses such as HIV or MLV.
  • HIV-GFP also called CS-CG
  • FuGENE® 6 Roche Applied Sciences
  • CS-CG HIV-GFP
  • FuGENE® 6 Roche Applied Sciences
  • a plasmid mixture containing 0.22 ⁇ g of CS-CG, 0.14 ⁇ g of pRK5/Pack1(Gag-Pol), 0.07 ⁇ g of pRK5/Rev, 0.07 ⁇ g of pMDG (VSV-G Env), and 0.5 ⁇ g of an APOBEC expression or empty vector control plasmid as described previously ( Liddament et al. (2004) Curr Biol 14:1385-1391 ).
  • virus-containing supernatants were clarified by low speed centrifugation, filtered (0.45 ⁇ m), and quantified using a reverse transcriptase activity based ELISA (Cavidi Tech).
  • Reverse transcriptase-normalized supernatants were applied to fresh 293T cells, and infection was allowed to proceed for 96 hr. Infectivity (GFP fluorescence) was then measured by flow cytometry (FACSCalibur, BD Biosciences).
  • the viral supernatants were treated with 50 units/ml DNase (Sigma) prior to 293T cell infection.
  • HsA3F and HsA3G caused 4- and 24-fold reductions in the infectivity of HIV-GFP. MmA3 also was capable of strongly inhibiting HIV-GFP.
  • expression of BtA3F, OaA3F or SsA3F caused 30-, 8- and 29-fold decreases in the infectivity of HIV-GFP, respectively ( FIG 15A ).
  • These potent anti-HIV activities demonstrated that the artiodactyl A3F proteins have at least one retrovirus restriction activity. These results further imply that the artiodactyl A3F proteins are able to specifically associate with the HIV Gag/genomic RNA complex and thereby gain access to assembling virus particles.
  • HIV-GFP infectivity also was monitored in the presence or absence of HIV-1 Vif and human, artiodactyl or mouse A3 proteins. Expression of HIV-1 Vif neutralized HsA3G and HsA3F (although the latter to a lesser extent) and caused a proportional recovery of HIV-GFP infectivity. Expression of HIV-1 Vif did little to enhance the infectivity of HIV-GFP produced in the presence of MmA3 or any of the artiodactyl A3F proteins. Thus, the artiodactyl A3F proteins were fully resistant to HIV-1 Vif.
  • MmA3 has little effect on the infectivity of MLV, presumably because MLV excludes (or simply avoids) this A3 protein ( FIG 15B ).
  • HsA3F and HsA3G inhibit the infectivity of MLV-based retroviruses, but to a lesser extent than HIV-based viruses ( FIG 15B ). Therefore, to begin to ask whether the artiodactyl A3F proteins possess broad, HsA3F- or HsA3G-like, or narrow, MmA3-like retrovirus restriction potentials, the infectivity of MLV-GFP produced in the presence of these A3 proteins was monitored.
  • N-terminal zinc-binding, deaminase domain of the artiodactyl A3F proteins catalyzes C -> U deamination
  • the GFP gene from the aforementioned HIV-GFP infectivity experiments was amplified by high-fidelity PCR, cloned and subjected to DNA sequence analyses. HIV-GFP produced in the presence of a control vector showed a low base substitution mutation frequency, 0.00014 mutations per base, which is attributable to errors in reverse transcription and PCR.
  • viruses produced in the presence of HsA3F, HsA3G, all three of the artiodactyl A3F proteins or MmA3 showed between 30- and 80-fold more base substitution mutations, which were almost exclusively retroviral G ⁇ A transition mutations.
  • HsA3G with a C-terminal domain E ⁇ Q mutation failed to cause retroviral hypermutation, although this variant still significantly inhibited HIV-GFP infectivity.
  • the HsA3F C-terminal zinc-binding domain mutant was still able to modestly inhibit HIV-GFP infectivity, without obvious signs of retroviral hypermutation.
  • HsA3F and HsA3G overwhelmingly preferred 5'-CC (84%) and 5'-TC (84%), respectively, whereas MmA3 preferred 5'-TC (61 %) and 5'-CC (29%).
  • the cow and the sheep A3F proteins appeared to prefer a pyrimidine (Y) 5' of the deaminated cytosine (93% and 79%, respectively).
  • the pig A3F protein preferred 5'-GC (47%). This is notable because this constitutes the only example of an A3 protein preferring 5'-purine-C (the immunoglobulin gene deaminase AID also has this preference).
  • all of the A3 proteins characterized in these analyses preferred a pyrimidine at the -2 position (which was invariably a T, except for HsA3G which preferred C > T).
  • Skin fibroblasts from a 9-year old prize boar were transfected with expression constructs encoding human APOBEC3F, human APOBEC3G, or both, and placed under G418 selection. Resistant colonies were picked and expanded. Colonies expressing the APOBEC3F, APOBEC3G, or both were identified by RT-PCR.
  • Groups of ova were transferred into 5 ⁇ l droplets of HEPES buffered NCSU-23 containing 10% fetal calf serum, 2.5 ⁇ g/ml cytochalasin B (CB) and 5 ⁇ g/ml Hoechst 33343, which were arranged in a column on the lid of a 9 mm x 50 mm Petri dish. Enucleation was achieved by physically removing the polar body and adjacent cytoplasm, containing the metaphase II plate, using an ES cell transfer pipette. Whole cell transfer was accomplished using an ES cell transfer pipette (Eppendorf, Westbury, New York) with a sharp, beveled tip (inner diameter 10 - 25 ⁇ m depending on cell type).
  • Donor cells i.e., transfected skin fibroblasts
  • presumptive G0/G1 by serum starvation (0.5%) for 24 h.
  • Microdrops containing oocytes were spiked with a small volume of donor cells that had been trypsinized not more than 3 h prior to enucleation.
  • couplets were fused within 2 h after enucleation.
  • Groups of 5-10 couplets were manually aligned between the electrodes of a 1 mm gap fusion chamber (BTX, San Diego, CA, USA) overlaid with mannitol fusion medium (0.28 M mannitol, 0.2 mM MgSO 4 x 7H 2 O, 0.01% PVA).
  • Couplets were fused by exposure to a single pulse of 150 V/mm for 60 us. Following fusion, couplets were cultured in HEPES buffered NCSU + 10% fetal calf serum from 0.5 to 1.5 h before activation. Couplets were activated by placing them in 1 mm gap fusion chamber overlaid with mannitol medium supplemented with 0.1 mM CaCl 2 x 2H 2 O and exposing them to two 60 microsecond pulses of 150V/mm.
  • Pubertal crossbred gilts aged 8 to 10 months were synchronized with Regumate (containing 0.4% altrenogest; 10 mg/day; Intervet, Boxmeer, Netherlands) mixed in commercial feed and given each morning for 17-19 days. All donor gilts were injected with 2,000 IU PMSG (Folligon & Chorulon) and 80 h later with 1,000 IU hCG (Folligon & Chorulon). Recipient gilts were injected with half the dosage of PMSG and hCG administered to the donors. Oocytes were surgically collected 46-50 h after hCG injection by flushing from the oviduct with HEPES buffered NCSU-23.
  • Recipient 2302 After waiting 20 minutes for the anesthesia to take effect, a high flank incision was made and both horns of the uterus were exposed. Neither horn contained any fetuses or mummies. However, the endometrium in both horns exhibited extensive cystic hyperplasia, which gave the uterus the appearance of being gravid. Recipient 2302 then was given a general anesthesia (acepromazine + ketamine) and euthanized. Recipient 2175 was also anesthetized and euthanized and her uterus examined for the presence additional mummies or fetuses; none were found.
  • Clones 5 (1200 g) and 6 (1200 g) were manually fed hourly, via syringe and mouse feeding needle, with Esbilac (milk replacement formula). Clone 6's health visibly improved during this nursing period, while clone 5's health declined. Clone 5 was extremely weak and no longer swallowing Esbilac and was euthanized the next day. Clone 6 was returned to his dam and was viable for 2 weeks, but had major abscesses on the tops of his rear feet and his swollen front pasterns. Daily injections of Tylan 200 and penicillin did not resolve this condition so the piglet was euthanized and cells were harvested.
  • Epigenetic reprogramming may be deficient in cloned embryos. Nuclei can be more effectively reprogrammed by passing them through multiple rounds of cloning and fetal fibroblast isolation before carrying piglets to term. Transgenic cells already produced can be used to generate reconstructed embryos, which would then be implanted and left to develop for about 40 days before the termination of pregnancy. Fibroblasts would then be isolated from these fetuses and cultured briefly before use in another round of somatic cell nuclear transfer to generate new piglets.
  • fetal fibroblasts Another alternative would rely on the use of fetal fibroblasts to start with, i.e., using fetal fibroblasts to generate new transgenic cells expressing the APOBEC proteins, and then generating pigs by somatic cell nuclear transfer as described above.
  • Most successful pig cloning experiments have utilized cells derived from fetal fibroblasts, as opposed to the aged boar used in this example.
  • Other sources of cells including embryonic or adult stem cells also can be used.

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